Abstract

Previously unreported CD8+CD28 and CD8+CD28+ T-cell subsets occur in healthy individuals and expand in patients suffering from autoimmune disease. Here we studied, for the first time, the expression of CD8+CD28+, CD8+CD28-, and CD8+CD56+ subpopulations in induced sputum from asthmatics. Using sputum samples, purified CD8+ T cells were stained for surface antigen CD28, CD56, FITC-conjugated anti-perforin, and anti-IFN-γ. Cytotoxic activity was evaluated in a chromium releasing test. Induced sputum CD8+CD28- T cells were found to be more expanded and expressed low levels of IFN-γ in severe asthmatics than mild asthma and age-matched healthy controls. The predominance of CD8+CD28- T cells can be in part explained by the expansion of CD8+CD56+. CD8+CD28- T cells from severe asthmatics produced high intracytoplasmic perforin and exerted a potent cytotoxic activity. Considering their phenotyping and functional properties, the CD8+CD28- T-cell subset may constitute an intermediate phenotype in the process of CD8+ T-cell differentiation of effector-type cells in severe asthmatics. Functional studies showed that CD8+CD28- T cells had cytotoxic function.